This invention relates generally to the hazardous condition detectors, and more specifically to the hush feature of such detectors.
In the past, many people died in their sleep because there was no warning system to awaken them during the early stages of a dwelling fire. Likewise, without a system that could detect the presence of a fire early in its development, many people were trapped in burning buildings once the fire escalated to a point that became easily detectable. Luckily, smoke detectors have been developed which reliably provide an early warning to individuals that a fire may be present. These smoke detectors are so effective in saving lives that they have been mandated as required appliances in many types of dwellings. Current smoke detectors utilize an Application-Specific Integrated Circuit (ASIC), such as the Motorola MC 14467. These ASIC""s and their corresponding analog circuitry allow for long battery life, reliable operation, and relatively low cost for these smoke detectors.
It goes without saying that to be effective a smoke detector must be operational. However, since smoke detectors are typically silent, consumers may not know whether or not their detector is operational. While many manufacturers include a feature that provides a periodic chirp as the battery is running low, many individuals desire the capability to affirmatively test the operability of their smoke detector. As such, modern smoke detectors include a push button that, when held in its actuated position, will place the smoke detector in a test mode of operation. This test mode will typically sound the smoke detector alarm after the test button is held for a period of two to three seconds.
While the alarm from a smoke detector is quite effective at warning occupants that smoke has been detected, such smoke does not always mean that a fire exists in the dwelling. Instead, the source of the detected smoke may be under the control of the occupant as, for example, in the situation where the occupant may be cooking in the kitchen. Occasionally, such cooking activities result in the generation of smoke to such a degree that the smoke detector is triggered. In such and other situations the sounding of the smoke detector alarm becomes more of an annoyance than a help.
To accommodate consumer desires to silence the alarm in such situations, while at the same time maintaining functionality of the smoke detector, a hush feature was introduced into conventional smoke detector design. Such a hush feature operates in conventional ASIC-based smoke detectors to reduce the sensitivity of the smoke detectors so that the smoke resulting from consumer-controlled conditions do not result in the sounding of the smoke detector alarm. In such a reduced sensitivity mode of operation, the conventional ASIC-based smoke detectors will sound an alarm if a level of smoke sensed continues to increase beyond the reduced sensitivity level. In this way, the consumers will again be provided with an audible warning indicating that the level of smoke within their dwelling has continued to increase since the hush feature was initiated.
While both the hush feature and the test feature satisfied consumer demands, many smoke detectors provided separate push-button switches to initiate these different modes of operation. Unfortunately, it was found that many consumers were inadvertently actuating the wrong push-button switch and, as a result, were confused by the subsequent operation of their smoke detector. As an example, if the hush button were actuated when the consumer actually wished to determine operability of the smoke detector by entering the test mode of operation, the alarm would not sound, possibly causing the consumer to believe that smoke detector is defective. Likewise, in the situation where the source of smoke is a known consumer-controlled event, actuation of the test button will not silence the smoke detector alarm as desired by the consumer. Such may result in the consumer believing that a larger problem exists within his dwelling, or that the smoke detector is malfunctioning. These problems in selecting the wrong switch are exacerbated by the fact that most smoke detectors are located on or near the ceiling where it is difficult to read the labeling provided for each of these two switches.
In an attempt to provide the desired functionality of both the test mode of operation and the hush mode of operation, many modern smoke detectors are beginning to utilize a single push-button switch, which is capable of actuating both the test mode and the hush modes of operation. One such detector having a hush feature is described in U.S. Pat. No. Re. 33,920 for a SMOKE DETECTOR HAVING VARIABLE LEVEL SENSITIVITY, issued to Tanguay et al. (hereinafter the Tanguay et al. ""920 patent). The Tanguay, et al. ""920 patent describes an application specific integrated circuit (ASIC) based analog smoke detector circuit having variable level sensitivity for allowing operation exclusively in a normal mode or in a hush mode, and having a test mode, both operable via a single switch.
The Tanguay, et al. ""920 patent utilizes a conventional smoke detector ASIC such as the Motorola MC14467. As is conventional with such a smoke detector ASIC, a reference voltage is supplied to pin P13 of the chip. This voltage input is coupled to an input of an analog voltage comparator within the ASIC, and establishes the alarm threshold value against which the output analog voltage from the smoke chamber 30 will be compared. The output voltage from a conventional ionization chamber is coupled to pin P15, which is the other input to the analog voltage comparator within the smoke detector ASIC. As is conventional with this type of device, when the voltage on pin P15 drops below the voltage on pin P13 the ASIC generates an output alarm signal to sound an audible alarm and to light a visible LED.
The smoke detector of the Tanguay, et al. ""920 patent also includes a user-actuated switch that initiates both a test mode and a hush mode of operation. Unfortunately, both modes of operation are always entered when the user-actuated switch is activated. That is to say, that hush mode of operation is actuated even if the smoke detector is not currently in an alarm condition and the user solely wishes to check the operability of the detector. In accordance with the teachings of Tanguay, et al. ""920, the detector test is initiated by contact of the user-actuated switch to the container of the ionization chamber. As described, this reduces the voltage supplied to the ionization chamber, resulting in a reduced output voltage therefrom. This reduced output voltage is sufficient for the smoke detector ASIC to generate an output alarm signal.
At the same time that the output from the ionization chamber is reduced due to the user-actuated switch completing a circuit to ground from the ionization chamber thereby reducing its input voltage, a test switch sensor circuit conducts current flow to an inhibit control circuit and a time constant circuit. These elements control the hush mode of operation once the user-actuated switch is released. Specifically, during actuation of the switch current flows into the time constant circuit to charge a capacitor through the test switch sensor transistor and a diode. Once the user releases the switch, the time constant circuit now begins operation by draining off the charge of the capacitor through the resistor divider network of R12 and R13. The voltage generated through this resistor divider network is sufficient to turn on the Darlington configured transistor, which reduces the voltage at pin P13. The level to which the voltage on pin P13 is lowered may be adjusted through the proper selection of resistors R15 and R16 and the transistor. These three elements form what is termed a sensitivity control means in the specification of Tanguay, et al. ""920. The Darlington configured transistor is referred to in the specification as a diminishing means which diminishes the sensitivity of the smoke detector in response to user actuation of the switch.
While the above-described system attempts to overcome certain problems in the art, it unfortunately introduces other problems that seriously compromise the effectiveness and operability of the detector. Specifically, the limitation that the ASIC introduces with regard to its ability to only sense a single threshold limits the detector to operation solely within the normal sensitivity mode of operation or the reduced sensitivity mode of operation, exclusively. The reduced sensitivity mode remains active even if the amount of smoke in the atmosphere reduces to the point where the normal alarm mode would not be entered. As such, the subsequent generation of a level of smoke that would sound the alarm in a normal sensitivity mode of operation will fail to do so because the detector continues to operate in the reduced sensitivity mode, even though the original condition necessitating the reduced sensitivity mode of operation has long since cleared.
The continued operation in the reduced sensitivity mode of operation highlights another shortcoming of the prior design in that it relies on external timing circuitry as the only mechanism for exiting the reduced sensitivity mode of operation. As described above, once this reduced sensitivity mode of operation has been entered, it will only be exited once the external time-delay circuitry has timed out, regardless of the atmospheric conditions existing within the environment of the detector. Further, while the above-described design attempts to simplify the user interface by providing a single switch to initiate both the test and the hush mode of operation, the use of an analog ASIC design results in both modes of operation being entered upon actuation of the single switch. That is, when the single switch is actuated, both the test mode of operation and the hush mode of operation are entered. As a result, the sensitivity of the detector is reduced even if the user merely wanted to test the operational readiness of the detector. The inadvertent entrance into the reduced sensitivity mode of operation will result in the detector having a reduced sensitivity to smoke for the entire period of the time-out delay.
There is a need existing in the art, therefore, for a smoke detector that utilizes a simplified user interface, but that provides selective initiation of the test mode of operation and the hush mode of operation. Further, there is a need existing in the art for a smoke detector that cancels the hush mode of operation in an intelligent fashion, or as a result of user de-selection thereof. In this way, the hush mode of operation is not continued when the conditions that necessitated its initiation no longer exist.
In addition to smoke detectors, recent advances in hazardous condition detection technology have allowed for the emergence of carbon monoxide detectors supplied to the general public. Such carbon monoxide detectors typically include a sensing element that provides an input to a microprocessor. The microprocessor calculates the total exposure dosage of CO through an accumulator function that correlates carbon monoxide concentration and exposure time. With continuing advances in the carbon monoxide detector technology, these detectors are now available at such a cost and with such a reliability that many manufacturers are now marketing combined smoke and carbon monoxide detectors for use in homes and dwellings.
However, these combination devices typically merely include a conventional ionizing-type smoke detector on the same chassis as a conventional carbon monoxide detector. These two detectors share the same power source and the same alarm system, but they typically independently perform sensing according to the technology of their individual, conventional sensors. Thus, the conventional combination smoke and carbon monoxide detector is not much more than an aggregation. That is, the two units will function independently through independent circuits to sense their independent parameters, but will use the same horn for the alarm. Indeed, the smoke detector portion of the combination units typically still utilizes the Application-Specific Integrated Circuit used in the individual units, and the carbon monoxide portion uses a separate microprocessor for calculating the accumulation dosage of carbon monoxide.
While such aggregate units are being marketed, the cost of these units still reflects the aggregation of both the ASIC and the microprocessor used for the separate smoke and carbon monoxide detection, respectively. Further, in order to allow for the accumulator to be reset a separate carbon monoxide detector reset switch is typically employed in these aggregate units. However, since the functionality of the CO detector is not integrated with the control of the smoke detector (and the initiation of the hush and test modes of operation), this results in two switches once again appearing on the combined detector. As discussed above, multiple switches on the detector may add to consumer confusion.
In view of the above, it is an object of the instant invention to provide a new and improved smoke detector overcoming the above described and other problems existing in the art. More particularly, it is an object of the instant invention to provide a new smoke detector having an intelligent hush feature and an intelligent test feature. It is a further object of the invention to provide such a detector that utilizes only a single button 18 to intelligently initiate either of these features.
It is an additional object of the invention to provide a combined smoke and carbon monoxide detector having these features. Further, it is an object of the invention that the control for both the smoke and CO detectors is integrated within a single microprocessor or microcontroller 12. It is an additional object of the instant invention to provide a combined smoke and CO detector that utilizes a single push button switch 18 to intelligently initiate the hush mode, the test mode, or reset the CO accumulator. Additionally, it is an object of the instant invention that initiation of any mode or reset of the accumulator will not inadvertently initiate any other mode of operation or inadvertently reset the accumulator.
Fundamentally, the hazardous condition detector of the instant invention represents an advance in technology that provides a more feature-rich detector than has previously been available. As described above, conventional smoke detectors are based on a special purpose ASIC that performs an analog comparison of the smoke chamber 30 voltage against a threshold, and generates an alarm based on the comparison. The new generation detector enabled by the instant invention will perform the comparison and alarm logic digitally in a microcontroller 12. Use of the microcontroller 12 will also allow a true combination detector for smoke and carbon monoxide (CO), in which a common microcontroller 12 handles measurement, calibration and alarm logic for both detectors.
With regard to the smoke detector specific aspect of the invention, additional functionality is provided. The capability to concurrently compare the smoke chamber 30 output with two or more thresholds, impossible in the conventional ASIC design as discussed above, provides a new form of self-clearing, intelligent hush. Conventional smoke detectors lose the ability to monitor the original alarm threshold when in the hush mode, and therefore must rely on a timer circuit to reset hush. In the detector of the instant invention, both the alarm and hush thresholds are concurrently monitored in hush, allowing the hush condition to self clear when the smoke clears from the detector. A digital timing function is provided as a backup to reset hush if the detector has not cleared within the UL mandated reset period. The user is also provided with the heretofore-unavailable option of entering or exiting hush by separately depressing the hush button 18 with an appropriate level of smoke detected. The test mode of operation is entered by depressing the push button switch 18 only if the detector is not in an alarm condition or the hush mode of operation.
With respect to the CO detector specific aspect of the invention, the resetting of the accumulator is accomplished via the same, single push button switch 18 as initiates the hush and test modes of operation. The selectivity provided by the common microcontroller 12 ensures that the accumulator is not inadvertently reset when the user is attempting to enter either the hush or test modes of operation. Specifically, the actuation of the user switch 18 resets the CO accumulator only if the detector is in a CO alarm condition. This selective, intelligent functionality is enabled by the use of a single microcontroller 12 for both the smoke and CO detector portions of the combined unit.
Other objects and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.